Emergency Medicine Hub / Toxicology & Environmental • 3 min read • 3 sections

Local Anesthetic Systemic Toxicity (LAST)

Comprehensive emergency resuscitation of Local Anesthetic Systemic Toxicity (LAST): unintentional intravascular injection and systemic absorption of amide (bupivacaine, ropivacaine, lidocaine) and ester local anesthetics, high-potency sodium-channel blockade and mitochondrial uncoupling, classic progression from perioral paresthesias and metallic taste to refractory status epilepticus and cardiovascular collapse, protocolized resuscitation with 20% Intravenous Lipid Emulsion (ILE/Intralipid), and essential ACLS modifications (low-dose epinephrine, avoiding vasopressin, calcium channel blockers, and beta-blockers).

Resuscitation Quick Actions • First 2 Minutes

High-Acuity

20% Lipid Emulsion Bolus

1.5 mL/kg IV bolus over 2–3 minutes (~100 mL in a 70 kg adult); repeat bolus once or twice for persistent cardiovascular collapse

ILE Maintenance Infusion

0.25 mL/kg/min IV infusion (~18 mL/min in 70 kg adult); continue for at least 10 minutes after hemodynamic stability is restored (max 10–12 mL/kg)

ACLS Epinephrine Dosing

REDUCE epinephrine doses to small boluses <= 1 mcg/kg (e.g., 50–100 mcg IV push); standard 1 mg doses worsen acidosis and impair lipid resuscitation

Drugs to AVOID

AVOID Vasopressin (causes pulmonary hemorrhage/vasoconstriction), Beta-blockers, CCBs, and Lidocaine/Procainamide (compounds toxicity)

First-Line Anticonvulsant

Benzodiazepines (Midazolam 5–10 mg IV or Lorazepam 2–4 mg IV); avoid propofol in hemodynamically unstable patients

Bupivacaine Lethality

Bupivacaine has a very low CC/CNS ratio (cardiovascular collapse occurs almost simultaneously with seizures, leaving no early warning)

Bottom-Line Clinical Pearl

LAST is a catastrophic complication of regional anesthesia, peripheral nerve blocks, or tumescent liposuction. Bupivacaine is the most cardiotoxic local anesthetic due to its high lipophilicity and slow dissociation from cardiac sodium channels ('fast-in, slow-out' kinetics). Early signs include circumoral numbness, metallic taste, tinnitus, and tremors, followed rapidly by seizures, conduction blocks, ventricular fibrillation, and asystole. The definitive antidote is 20% Intravenous Lipid Emulsion (ILE): bolus 1.5 mL/kg IV over 2–3 minutes, followed by an infusion of 0.25 mL/kg/min. Modify ACLS: reduce epinephrine doses to < 1 mcg/kg (avoid standard 1 mg doses) and avoid vasopressin, beta-blockers, and calcium-channel blockers.

1. Pathophysiology: Voltage-Gated Sodium Blockade & Lipid Sink

Local anesthetics block voltage-gated fast sodium channels in excitable neuronal and myocardial membranes, halting depolarization and action potential propagation. When systemic absorption or accidental direct intravascular injection occurs, toxicity manifests in the central nervous and cardiovascular systems.

Bupivacaine Cardiotoxicity: Highly lipophilic agents such as bupivacaine exhibit intense affinity for inactivated cardiac sodium channels with exceptionally slow dissociation kinetics ('fast-in, slow-out'). This causes widening of the QRS complex, PR prolongation, AV dissociation, intractable re-entrant ventricular tachyarrhythmias, and profound myocardial contractility depression.

Mechanisms of 20% Lipid Emulsion Therapy: ILE functions via both a 'lipid sink/metabolic shuttle' (partitioning the lipophilic local anesthetic molecules away from myocardial and brain tissue into a newly created plasma lipid compartment) and a direct metabolic/inotropic effect (delivering fatty acid fuel directly to ischemic cardiomyocytes and reversing local anesthetic-induced inhibition of mitochondrial carnitine-acyltransferase-1).

2. Clinical Stages of Toxicity

Progression Stage	Clinical Manifestations	Diagnostic & Resuscitative Priorities
Early Central Nervous System	Circumoral numbness, tongue paresthesias, metallic taste, tinnitus, lightheadedness, auditory hallucinations, slurred speech	Stop local anesthetic injection immediately; alert resuscitation team; place on continuous cardiac monitor and supplemental oxygen.
Excitation/Hyperactivity	Facial twitching, myoclonic jerks, agitation, confusion, generalized tonic-clonic status epilepticus	Benzodiazepines immediately (Midazolam 5–10 mg IV); secure airway to prevent hypercapnia and acidosis (acidosis worsens local anesthetic dissociation).
CNS Depression	Lethargy, coma, respiratory arrest, loss of airway reflexes	Endotracheal intubation with lung-protective ventilation; prepare 20% Intralipid.
Cardiovascular Collapse	Bradycardia, conduction blocks, wide QRS, ventricular tachycardia, torsades de pointes, ventricular fibrillation, asystole	Initiate modified ACLS and start 20% Intravenous Lipid Emulsion immediately; contact ECMO/perfusion team.

3. The ASRA Lipid Emulsion Protocol

Phase of Protocol	20% Lipid Emulsion Dosing	Critical Clinical Actions
Initial Bolus	1.5 mL/kg IV bolus over 2 to 3 minutes (~100 mL in a 70 kg patient)	Administer immediately upon identification of cardiovascular collapse or prolonged seizures.
Continuous Infusion	0.25 mL/kg/min IV infusion (~18 mL/min in 70 kg patient)	Start immediately following bolus; continue for at least 10 minutes after hemodynamic stability is restored.
Repeat Bolus (If Unstable)	Repeat 1.5 mL/kg bolus once or twice every 3–5 minutes	Can increase infusion rate to 0.5 mL/kg/min if hypotension persists.
Maximum Safe Dose	12 mL/kg total over the first 30 minutes	Avoid exceeding maximum cumulative dose to prevent acute pancreatitis and fat overload syndrome.

Critical Pitfall / Contraindication

CRITICAL ACLS MODIFICATIONS IN LAST: During cardiopulmonary resuscitation for local anesthetic toxicity, REDUCE standard epinephrine boluses to <= 1 mcg/kg (e.g., 50–100 mcg IV push). Animal and clinical studies demonstrate that standard 1 mg epinephrine doses exacerbate myocardial acidosis, induce intractable tachyarrhythmias, and impair lipid emulsion-mediated resuscitation. Furthermore, DO NOT USE vasopressin, calcium channel blockers, beta-blockers, or additional local anesthetics (e.g., lidocaine).

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